Comcast details BitTorrent 'delay' tactics

Responding to August's landmark order from the FCC, Comcast has provided an extensive description of its infamous BitTorrent blocking - though it has yet to admit that blocking is the right word.

According to a statement (PDF) filed Friday with the FCC, the big-name ISP began using a traffic switch from Sandvine Inc. in May 2005 in an effort to determine which protocols were causing congestion on its cable-based network. These tests pinpointed several peer-to-peer protocols - including BitTorrent, eDonkey, FastTrack, and Gnutella - and sometime in 2006, the company began using the Sandvine switch to throttle them.

"Commercial (i.e. not trial) deployment of this equipment took place over an extended period of time, beginning in 2006," the statement reads. "We achieved wide-scale deployment in 2007." In November 2007 - after its use of Sandvine was exposed - the company began throttling the Ares protocol as well.

The statement goes on to say that Sandvine's equipment "has been used (1) to determine when the number of simultaneous undirectional upload sessions for a particular geographic area reaches [a] pre-determined threshold, and (2) when a threshold is reached, to temporarily delay the initiation of any new unidirectional upload sessions for that protocol until the number of simultaneous unidirectional upload sessions drops below that threshold."

Comcast also specifies the thresholds for each of the five P2P protocols being throttled.

After an independent network researcher revealed the company's P2P throttling in May 2007, Comcast flatly denied it. And though it eventually acknowledged the basic practice, it has always said that it "temporarily delays" P2P uploads rather than blocking them. But this is misleading.

Using Sandvine's equipment, Comcast sends reset packets that prevent one machine from connecting to another. And if the number of uploads drops below Comcast's threshold, these connections are not reinstated. In other words, they're blocked, not delayed.

In early August, after a 3-2 split decision, the FCC's five commissioners told the world that Comcast had violated its Internet Policy Statement, ordering the company to completely disclose its discriminatory network management practices and how it intends to stop these practices by year's end.

A month later, Comcast appealed in federal court, but said it would comply with the order. Thus today's filing.

In the filing, Comcast says that P2P accounts for half of all upstream traffic on its network and that in some locations, it accounts for two-thirds of the traffic. Then it says that 90 per cent of this P2P traffic isn't throttled. ®